Monolithic microwave integrated circuits (“MMICs”) are widely used in commercial and military microwave systems. Due to the fine geometry used in MMIC transistors, these circuits are susceptible to damage from high-power spurious electromagnetic radiation, e.g., from microwave transmitters or nuclear electromagnetic pulses. In particular, low-noise amplifiers (“LNAs”) in the front-end of such microwave systems need high-power protection because these amplifiers can typically sustain only input power levels in the range of 10 to 20 dBm for a continuous-wave (“CW”) input signal, or from 1 to 3 μJ for a pulsed input signal. For this reason, many radar, electronic warfare (“EW”), navigation and communication systems require ultra broadband high power limiters with low insertion loss, fast recovery time and low leakage output power. At present, however, no broadband 10-W CW limiter product is available that is capable of working over a 2-20 GHz frequency band.
Existing broadband limiter products are typically capable of handling only about one to three watts of CW power, and have a high insertion loss of about 2 dB, a long recovery time of about 1000 ns (or about 1 μs) and a high leakage output power of about 20 dBm. To protect highly sensitive MMIC circuits, however, a high power limiter with less than 0.3 dB insertion loss is needed. Moreover, it is desirable for the power limiter technology to be compatible with existing LNA technology (typically GaAs), so that the limiter circuit may be integrated onto the same GaAs chip as the LNA circuit. Finally, good broadband performance of the limiter is also a requirement in order to cover the frequency range of operation.